Background: Enthesitis or inflammation of tendon/ligament anchorage points is the cardinal lesion in spondyloarthritis (SpA). Through the use of cytokine targeting biologics and also murine models, several key mediators have been shown to have a role in enthesitis, such as IL-23/17 axis and TNF ¹ . We have previously shown that the human enthesis contains myeloid cells capable of IL-23 and TNF production and range of T-cells capable of IL-17A/F secretion ^2,3 . Attempted inhibition of p38 MAPK for inflammatory disease in the past has yielded toxicity issues. The MAPK-associated protein kinase 2 (MK2) is situated downstream of p38 MAPK, relaying the phosphorylation signal to the nucleus, and is thus a promising target.

Objectives: To determine if a novel MK2 inhibitor (MK2i) could supress innate and adaptive immune responses in an in vitro human enthesis model.

Methods: Normal spinous process enthesis was obtained from patients undergoing spinal decompression or surgery for scoliosis correction. Following enzymatic digestion, entheseal cells (n=5) were harvested and stimulated either with LPS/IFNγ (Entheseal myeloid cell activator) or anti-CD3 (Entheseal T-cell activator) with and without MK2i (1, 0.1 and 0.01µM) for 24 hr. Supernatant was harvested and protein detected using multiplexing for panels relating to inflammation (IL-1β, IFN-α2, IFN-γ, TNF, CCL2, IL-6, IL-8, IL-10, IL-12p70, IL-17A, IL-18, IL-23, and IL-33) or T-cell activation (IL-2, IL-4, IL-5, IL-6, IL-9, IL-10, IL-13, IL-17A, IL-17F, IL-22, IFN-γ and TNF).

Results: Following LPS/IFNγ stimulation of entheseal cells, 1µM MK2i significantly attenuated secretion of TNF, IFNα, IL-6, IL-10, IL-8 and CCL2. Several other targets did not reach statistical significance, but trended downwards with inhibition such as IL-1β, IL-12 IL-18 and IL-33. Following Entheseal T-cell activation by anti-CD3 stimulation, 1µM MK2i supressed TNF and IL-17A.

Conclusion: MK2i suppressed LPS driven production of several disease relevant mediators such as TNF. MK2i also supressed anti-CD3 induced T-cell derived mediators such as TNF and IL-17A. MK2 inhibition is a promising novel therapeutic target in the treatment of Spondyloarthritis.

REFERENCES:

[1]Bridgewood, C., et al., Spondyloarthritis: new insights into clinical aspects, translational immunology and therapeutics . Current opinion in rheumatology, 2018. 30 (5): p. 526-532.

[2]Bridgewood, C., et al., Identification of myeloid cells in the human enthesis as the main source of local IL-23 production . Annals of the rheumatic diseases, 2019. 78 (7): p. 929-933.

[3]Cuthbert, R.J., et al., Evidence that tissue resident human enthesis γδT-cells can produce IL-17A independently of IL-23R transcript expression . Annals of the rheumatic diseases, 2019. 78 (11): p. 1559-1565.

Disclosure of Interests: Charlie Bridgewood: None declared, Chi Wong: None declared, Rajula Gaur: None declared, Francisco Ramirez-Valle: None declared, Dennis McGonagle Speakers bureau: AbbVie, Celgene, Janssen, Merck, Novartis, Pfizer, UCB, Consultant of: AbbVie, Celgene, Janssen, Merck, Novartis, Pfizer, UCB, Grant/research support from: AbbVie, Celgene, Janssen, Merck, Pfizer